1. Field of the Invention.
The field of the invention relates to a ventilating support for roof insulation and more particularly to a ventilating support which permits air to circulate at the interface between the roof insulation and a roof deck to inhibit the accumulation of moisture.
2. Description of the Prior Art.
The prior art recognizes that roof insulation of solid construction such as boards, will collect moisture at the interface between the roof deck and the facing surface of the board. Accumulated moisture can cause deterioration to and loss of the deck material through rot, if made of wood, or corrosion, if made of metal.
Corrugated metal roof decks, as shown, for example, in U.S. Pat. Nos. 4,073,997, and 3,029,172, illustrate flutes provided as part of the deck corrugation through which air may pass to prevent moisture from collecting. This configuration in combination with roof vents is helpful in the removal of moisture. However, as may be seen, air flow is only unidirectional along the central longitudinal axis of the flute. On a flat roof deck with a solid board not even a unidirectional passageway is available.
It is also known to provide a rough texture or bidirectional grooves on the roof deck facing surface of insulation board to permit omnidirectional air flow whether or not the board is applied to a corrugated roof deck or to a flat one. In this regard see, for example, U.S. Pat. No. 3,455,076, July 15, 1969, and Canadian No. 712,301. Canadian No. 712,301 teaches, in FIG. 3, for example, a cross-directional configuration consisting of a multiplicity of "V" shaped flutes which intersect at right angles to each other leaving a series of elongated truncopyramidal shaped bosses closely arranged with each other such that the base of each boss coincides with and is defined by the edge of the base of each adjacent boss. Such arrangements allow the unrestricted passage of air along the flutes so long as care is taken to align adjacent boards, flute to flute, during installation or, as is common in ordinary installations, so long as cut-to-size and fitted boards are not used. When care is not taken, flutes can be blocked by misalignment resulting in unvented or dead air pockets where moisture can accumulate. Therefore, the installer of this type of insulation must be sure that the boards are aligned properly in order to avoid pockets of dead air.
U.S. Pat. No. 3,387,420 discloses an insulating sheet which permits ventillation and avoids the possible dead air pockets of the Canadian Pat. No. 712,301. This is accomplished by spacing the insulating boards from each other so that none of the ventillating passagewayes between adjacent boards can be blocked. Unfortunately, the space left between boards has no insulation even though the spaces may be sealed by selvage strips (19b in FIG. 5) which overlaps adjaced boards.